Many types of vehicular crash sensors have been proposed and used for determining if a crash involving the vehicle is severe enough to require the deployment of a passive restraint system such as an air bag or seat belt tensioner.
Three types of sensors have been widely used to sense and initiate deployment of an air bag passive restraint system. These sensors include an air damped ball-in-tube sensor such as disclosed in U.S. Pat. Nos. 3,974,350, 4,198,864, 4,284,863, 4,329,549 and 4,573,706 (all in the name of Breed), a spring mass sensor such as disclosed in U.S. Pat. Nos. 4,116,132 and 4,167,276 (both in the name of Bell) and an electronic sensor such as is now part of several air bag systems. Each of these sensors has particular advantages and shortcomings that were discussed in detail in U.S. Pat. No. 4,995,639 referenced above.
The use of tape or ribbon switch technology as a crush switch was also disclosed in the '639 patent. Further research has shown that an improvement of this particular implementation of the invention has significant advantages over some of the other implementations since the switch can be easily made long and narrow and it can be made to respond to bending. In the first case, it can be designed to cover a significant distance across the vehicle which increases the probability that it will be struck by crushed material or bent as the crush zone propagates rearward in the vehicle during a crash. In the second case, it can be made small and located to sense the fact that one part of the vehicle has moved relative to some other part or that the structure on which the sensor is mounted has deformed.
Other crush zone mounted crash sensors including crush switch designs where the width and height dimensions are comparable, must either be large and thus heavy, expensive and difficult to mount, or there is a possibility that the randomly shaped crushed material which forms the boundary of the crush zone will bridge the sensor resulting in late triggering. This crushed material frequently contains holes, wrinkles or folds or portions that may even be displaced or torn out during the crash with the result that it is difficult to guarantee that a particular small area where the sensor is mounted will be struck early in the crash.
A significant improvement results, therefore, if the sensor can stretch across more of the vehicle or if it can determine that there has been relative motion or deformation of a portion of the vehicle on which the sensor is mounted. The improved sensors described herein are small in height and thickness but can extend to whatever length is necessary to achieve a high probability of a sensor triggering on time in a crash. A short sensor can be used if it is carefully mounted onto portions of the vehicle that will cause the sensor to bend during a crash.
It has been found that conventional designs of tape or ribbon switches have the drawback that the force required to close the switch is very small compared with the forces which are normally present in automobile crashes. During routine maintenance of the vehicle, the normal tape switch may be damaged or otherwise made to close and remain closed, with the result that later, when the vehicle encounters a pot hole or other shock sufficient to cause the arming sensor to close, an inadvertent air bag deployment can result. Similarly, if the tape switch is mounted on the front of the radiator support, which is a preferred mounting locating for crush zone sensors, hail, heavy rain, stones or other debris from the road might impact the tape switch and cause a momentary closure or damage it. If this happens when the vehicle experiences a shock sufficient to cause the arming sensor to close, an inadvertent air bag deployment might also occur. The force typically required to close a tape switch is less than one pound whereas tens of thousands of pounds are required to stop a vehicle in a crash and local forces greatly in excess of 20 pounds are available to actuate a sensor during a crash.
The present invention seeks to eliminate these drawbacks through the use of a tape switch design that requires either a large force to actuate or a bending of the switch due to structural deformation as explained below.
In 1991, the inventor of the current invention published a paper titled "A Critique of Single Point Sensing", SAE 920124, 1992, which is included herein by reference, where the authors demonstrate that there is insufficient information in the non-crush zone of the vehicle to permit a decision to be made to deploy an airbag in time for many crashes. The CrushSwitch.TM. crash sensors described herein and in U.S. Pat. No. 5,441,301 to Breed et al., provide an apparatus and method for determining that the crush zone of the automobile has undergone a particular velocity change. This information can be used by itself to make the airbag deployment decision. As airbag systems become more sophisticated, however, the fact that the vehicle has undergone a velocity change in the crush zone can be used in conjunction with an electronic sensor mounted in the passenger compartment to not only determine that the airbag should be deployed but an assessment of the severity of the crash can be made. In this case, the front crush zone mounted sensor of the type disclosed herein can be used as an input to an electronic algorithm and thereby permit a deployment strategy based on the estimated severity of the accident. Although the sensors described herein are one preferred approach of providing this capability, the sensors disclosed in the above referenced patents would also be suitable. Alternately, in some cases, sensors of another design can fulfil this function. Such sensors might be based on the electromechanical technologies such as the ball-in-tube sensor described in U.S. Pat. No. 4,900,880 or in some cases even electronic sensors could be used as crush zone mounted sensors for this purpose.